Wake Forest Physics
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WFU Physics Ph. D. Thesis Defense
TITLE:
Measuring the Microscale Mechanical Properties of Fibrin Fibers
and Cancer Cells
SPEAKER:
Justin Sigley,
TIME: Monday November 11, 2013 at 11 AM
PLACE: Room 103 Olin Physical Laboratory
ABSTRACT
The microscale material properties dictate the macroscale behavior of
biological systems. Fibrinogen, one of the most abundant proteins in the
blood, is converted into fibrin fibers that perform the essential
mechanical task of stemming the flow of blood. Fibrinogen fibers can be
fabricated by a technique called electrospinning. We studied the
mechanical properties of dry, electrospun fibrinogen fibers using a
combined atomic force/fluorescence microscopy technique. The mechanical
properties of these electrospun fibers is important due to their potential
use in tissue engineering and their biocompatibility. The same atomic
force/fluorescence microscopy technique is used to measure the mechanical
properties of fibrin fibers formed from patient plasma. The mechanical
properties of blood clots have been related to diseases such as
cardiovascular disease and diabetes, but the mechanisms responsible for
their mechanical properties are not well understood. The glycation of
fibrinogen, a marker for glycemic control in diabetic patients, did not
affect the mechanical properties of individual fibrin fibers. The modulus
of the fibers was found to be directly related to the diameter of the
fibers and provides evidence for a non-uniform density of protofibrils
within the fiber.
Cancerous and non-cancerous cells have different
mechanical properties arising from biochemical alterations as normal cells
transform to cancer cells. This transformation may affect the mobility of
proteins and small molecules within the cell. We used a novel technique
called Raster Image Correlation Spectroscopy (RICS) to measure the
diffusion coefficients of fluorescent proteins in living cells. We found
the diffusion coefficients of these proteins are not affected by
neoplastic transformation in the cytoplasm, but the mobility of the
fluorescent proteins is altered in the nucleus of the cells. This suggests
neoplastic transformation alters the intra-nuclear structure on a length
scale similar to the sizes of the proteins measured. We cross-validated
the RICS results with Fluorescence Recovery After Photobleaching (FRAP)
experiments. The RICS and FRAP results agree in 87% of the measurements.
We then demonstrate the accuracy of RICS measurements by performing a RICS
analysis on quantum dots undergoing a programmatically controlled 2D
random walk. Direct confirmation of RICS results provides progress toward
a gold standard for molecular dynamics measurements in live cells.
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